An X-ray CT apparatus provides information on an object through an image on the basis of intensity of X-rays having passed through the object, and plays an important role in lots of medical practices such as diagnosis and treatment of disease, surgery planning, etc.
The X-ray CT apparatus includes a multislice CT (ADCT: area detector computed tomography) apparatus having a multislice detector. A helical scan of a spherical or domed object done by the use of a multislice CT apparatus causes windmill artifacts to appear on an image. The windmill artifacts are brought about by data of a plurality of columns of detecting elements incidentally just matched with one another in reconstruction. As the multislice CT apparatus does not use the same detecting element around 360 degrees all the time in the reconstruction and interpolates data between the detecting elements correspondingly to an angle, it looks as if the data on the respective columns of the detecting elements crosses over to one another. As there is a plurality of thresholds of crossing over, the windmill artifacts appear on the image.
Incidentally, a technology for reducing windmill artifacts by filtering raw data is known as art related to the invention. In this technology, a method for filtering data in a direction of columns being channel-dependent is introduced so that windmill artifacts can be dealt with in a helical scan.
The windmill artifacts are not specific to the helical scan, and conspicuously appear particularly on a cone angle end in circular orbit (CFK: circular feldkamp) reconstruction in a conventional scan. A reason for that is undersampling in the column direction similarly as in the helical scan, and requires a flying focus in the column direction so as to be solved in principle.
In the circular orbit reconstruction in the conventional scan, as described above, windmill artifacts are likely to appear not in the center of the cone angle in principle but from the central column to the end column in the multislice detector conspicuously. Thus, if the ordinary art in the helical scan is applied to the conventional scan for raw data produced close to the end column apart from the central column in the multislice detector, an effect on reduction of artifacts can be obtained on images.
If, however, the ordinary art in the helical scan is applied to the conventional scan for raw data produced close to the central column in the multislice detector, an area where no windmill artifacts appear is processed as well, resulting in that an image obtained by a detecting element in a column close to the central column in the multislice detector undergoes careless degradation of space resolution.